"I go to the Heath to be somewhere that feels natural," writes Andy Sewell in the succinct introduction to his book of photographs of Hampstead Heath, "but I know this is no pathless wood. The Heath is as managed as any other part of London, but managed to feel wild."

It is this hinterland between the created and the natural that Sewell captures in his images of the giant swaths of grassland and woodland that draws Londoners to its winding paths and quiet, almost wild places. For Sewell, the Heath is "a place to get lost in – if only briefly". It is also a quietly mysterious landscape, especially at dusk when the shadows lengthen and deepen. It was on one of its winding paths that the narrator of Wilkie Collins's classic novel The Woman in White meets the spectral Anne Catherick skulking in the shadows. Collins captures the Heath, a countryside in the heart of the city, in all its inbetweeness: "The evening, I remember, was still and cloudy; the London air was at its heaviest; the distant hum of the street-traffic was at its faintest; the small pulse of the life within me, and the great heart of the city around me, seemed to be sinking in unison, languidly and more languidly, with the sinking sun."

You can sense that feeling of calm and sanctuary, of the city receding, in Sewell's photographs. He spent five years prowling the Heath with his camera, much of that time spent waiting patiently. He has an eye for evocative detail: a crimson net of peanuts dangling from a branch on which an expectant blue tit waits; an ominous cross carved into the bark of a tree; a small mound of sand amid branches and bracken that looks like a burial mound. This is the Heath as a living landscape but also as a mood and an atmosphere. Two crows perch on a bench, surrounded by burnished grass, the city lurking in the misty distance like a faraway place.

Sewell's camera captures the passing seasons, often intricately and evocatively: ice covers and stills the surface of a pond, the sun brings out dog walkers who congregate on a meadow as manicured as a lawn. Sometimes he looks at the landscape from a Martian's point of view: a giant snowball looks like a piece of a meteorite; a swimmer in Hampstead ponds resembles a dead body suspended in viscous, rain-dappled water. Here and there, people lurk or linger, and a mysterious figure appears amid the shadows in a green glade. This is a book of suggestion, a landscape of the imagination as well as a record of a real and familiar place. A classic of understated observation.